As for electrophotographic photoreceptors, inorganic photoreceptors principally comprising an inorganic photoconductive material such as selenium, zinc oxide or cadmium sulfide have widely been used so far.
However, these inorganic photoreceptors have not always been satisfactory in their characteristics such as photosensitivity, thermal stability, moisture resistance and durability each required for copiers. For example, selenium is liable to deteriorate the characteristics for an electrophotographic photoreceptor, because selenium is crystallized by heat or a finger print stain. And, an electrophotographic photoreceptor applied with cadmium sulfide has been deteriorated in moisture resistance and durability. Further, an electrophotographic photoreceptor applied with zinc oxide has had a problem in durability. Still further, an electrophotographic photoreceptor applied with selenium or cadmium sulfide has also had a defect that they have been seriously limitative to their manufacture and manipulation from the viewpoint of toxity.
For improving the above-mentioned defects of the inorganic photoconductive materials, many studies have positively been made in recent years and the attempts were made to use various organic photoconductive materials in the photoreceptive layers of electrophotographic photoreceptors. For example, Japanese Patent Examined Publication (hereinafter referred to as JP Examined Publication) No. 50-10496/1975 describes an organic photoreceptor containing both polyvinyl carbazole and trinitrofluorenone. However, the photoreceptor described therein is not satisfactory for photoreceptivity and durability. Therefore, a function-separated type electrophotographic photoreceptor has been so developed as to assign the roles of a carrier-generating function and a carrier-transport function separately to the different materials, respectively.
In such an electrophotographic photoreceptor as mentioned above, the materials may be selected out of the wide ranges of them, so that any desired characteristics may be provided. It has, therefore, been expected to provide an organic photoreceptor high in photoreceptivity and excellent in durability.
As for the carrier-generating materials and the carrier-transport materials for the above-mentioned function-separated type electrophotographic photoreceptors, a variety of organic compounds have been proposed. Many carrier-generating materials have been put to practical application. They include, for example, a polycyclic quinone compound typified by dibromoanthanthrone, a pyrylium compound, an eutectic complex of a pyrylium compound and a polycarbonate, a squarium compound, a phthalocyanine compound and an azo compound. And, many carrier-transport materials have been put to practical application. They include, for example, a pyrazoline compound, a polyaryl alkane compound, a triphenylamine compound, a hydrazone compound, a diaminobiphenyl compound and a styrylbenzene compound.
Among the above-given compounds, JP Examined Publication No. 61-8423/1986 (U.S. Pat. No. 3,972,717) discloses a technique in which the perylene compounds represented by Formula [I] and/or [II] which are one of the elements constituting this invention are used as the carrier-generating materials of electrophotographic photoreceptors.
After this disclosure was made, the techniques of combining the carrier-generating materials with many kinds of carrier-transport materials have been reported. There are known techniques, for example, Japanese Pat. Publication Open to Public Inspection (hereinafter referred to as JP OPI Publication) No. 59-59686/1984 discloses a combination with a pyrazoline compound and a hydrazone compound, JP OPI Publication Nos. 61-275858/1986 (USP 4,587,189) and 63-180956/1988 disclose each a combination with a benzidine compound, JP OPI Publication No. 63-291061/1988 discloses a combination with a butadiene compound and USP-5,019,473 discloses a combination with a diphenyl methane compound.
As indicated above, some attempts have so far been tried. In the copiers, printers and facsimile equipments of the electrophotographic system, the demands for making faster in operations and smaller in sizes have recently been getting more serious. And, the photoreceptive materials have been more demanded to be improved in photosensitivity and, at the same time, to be made faster in photoreception response as a line speed is increased and a photoreceptive drum is made smaller in size. Therefore, the functional characteristics have not been satisfactory to meet the above-mentioned demands in any conventional techniques.